1. Technical Field of the Invention
The present invention relates to a multichannel electronic-ignition control device with high-voltage controller.
2. Description of Related Art
As is known, electronic-ignition devices are used for generating sparks between two electrodes and thus sparking off combustion of a gas or of a mixture of air and a fuel set in the proximity of the electrodes. A very common example of application of electronic-ignition devices, to which reference will be made hereinafter (without this, however, being considered in any way limiting) regards the field of controlled-ignition internal-combustion engines. In this case, the sparks produced are used for sparking off combustion of the air-fuel mixture inside each of the cylinders of the engine.
Normally, electronic-ignition devices comprise a control circuit and a power switch, such as for example an insulated-gate bipolar transistor (IGBT). As is known, the power switch is controlled so as to open and close, alternately, the connection between a supply source (battery) and the primary winding of a transformer, which has a secondary winding connected to a spark plug, where the electrodes for generation of sparks are located. In particular, in a first stage, the power switch closes the circuit, and a current that increases in time in a substantially linear way starts flowing in the primary winding. Next, the power switch is re-opened, interrupting sharply the current flow in the primary winding and causing a voltage peak, which is transferred to the secondary winding. Thanks to the advantageous ratio between the number of turns of the primary winding and the number of turns of the secondary winding (for example 1:100), the amplitude of the voltage peak on the secondary winding is markedly increased and is sufficient for generating an electric arc between the electrodes of the spark plug.
In order to reduce the overall dimensions and the costs of fabrication of electronic-ignition devices, solutions have been proposed that envisage the use of a single multichannel control device, controlling a plurality of power switches. In particular, the control device must supply control voltages normally of about 10–15 V to the power switches and hence may be made in a first semiconductor wafer using standard techniques for the fabrication of semiconductors. The power switches, instead, have to withstand voltages of 250–600 V and hence have to be made in separate semiconductor wafers, using special technologies for preventing the risk of breakdown.
Multichannel electronic-ignition devices of the type described, however, suffer from a number of serious limitations. In fact, the control circuit cannot interact with the high-voltage terminals of the power switches, because it is unable to withstand the voltage peaks necessary for generation of the sparks. Consequently, it is not possible to intervene in order to attenuate the undesired effects which are normally associated to power components. In certain operating conditions, in particular, the high-voltage terminals of power switches may oscillate and need to be stabilized. Otherwise, in fact, the oscillations may have an amplitude sufficient for producing undesirable sparks, thereby causing serious problems. In addition, it may be necessary to drive the power switches so as to cause gradual and controlled discharge of the energy stored in the windings of the transformer if any malfunctioning is identified. Also the immediate opening of the circuit by the power switches could in fact produce undesirable sparks.
There is a need in the art to provide an electronic-ignition control device which is free from the drawbacks described above.